Mandrel for making pipe bends



Nov. 28, 1939. J. H. TAYLOR 2.1813

MANDREL FOR MAKING RIPE BENDS Filed Jan. 15, 1938 Patented Nov. 28,1939

UNITED STATES PATENT OFFICE 1 Claim.

My invention relates to the manufacture ofpipe fittings and presents a new mandrel for the forming of pipe bends, such as elbows and U- turns.

The method of feeding straight pipe of given diameter to a curved enlarging mandrel, and drawing it over' the same, forming a bend of greater diameter, is well known. 7

The object of my invention is to provide a mandrel, whereby substantially uniform wall thickness is preserved and whereby the displacement of metal is reduced to a This object I attain by so calculating the mandrel that, constantly as the movement of pipe over the mandrel proceeds, the upsetting resulting from the curving thereof is substantially balanced by the stretching due to increase of diameter.

My invention is illustrated in the accompanying drawing, in which- Figure 1 is an elevational view of the mandrel, with pipe, shown in section, being forced over it,

and

Figure 2 is an elevational view of the mandrel normal to the elevation of Figure 1.

The mandrel, indicated ata, of circular crossthe straight portion b for the attachment of an operating rod. The pipe is shown at e, and it will be understood that the mandrel is pulled through the pipe in the direction of the arrow, f, or the pipe is pushed over the mandrel in the direction of the arrow g, ,or both may be moved in such relative directions.

The straight pipe fed to the mandrel is of given wall thickness and diameter,v and the straight portion of the mandrel fits snugly therein.-

The mandrel begins to curve and enlarge at the,.transv erse plane indicated by the dot-anddash line o--h, andthe point 0 is the point from which the outer curve 2' of the, mandrel is subscribed, tangent to the straight line 7' on the surface of the straight portion of the mandrel, this curve representing the desired outer curve of, the

bend to be formed.

diameter from the plane oh-to the plane o-Jc is reflected in a distorted inner curve I. My invention-is concerned with the determination .of

this particular inner curve and th'e'shape of the mandrel. follows from that determination.

This inner curve I is determined as-followsz The arc between planes o-h-and o-k may be considered as divided into an infinite number of units of curvature and ,an infinite [number of units of diameter increase. For practical purposes, the arc is divided into a multiplicity of equal parts, each representing a certain amount of curvature, which is reflected in longitudinal offsetting of metal in the pipe wall, and to each part is assigned diameter increase the ratio of which to the total diameter increase is the same as the ratio of each part to the total are, such diameter increase reflecting itself in circumferential stretching of the metal in the pipe wall.

For instance, the illustrated are between the mandrel diameter for each plane to the next is section, comprises the straight portion b, the curved portion 0, and means d, at the free end of I 23' Accordingly, each unit of movement of the pipe over the mandrel results'simultaneously in uniform longitudinal offsetting and uniform circumferential stretching. The outer curve of the pipe is as if it were simply bent about the outer curve of the mandrel, the ofisetting graduating from zero at the outer curve to maximum at the inner curve, and the circumferential stretching being constantly in approximate balance with the longitudinal offsetting.

From the plane ok to the free end of the curved portion of the mandrel, the diameteris uniform and is the desired internal diameter of the fitting to be formed, the inner curve being over the radius 1/.

As the pipe'leaves the mandrel, elbows and U- turns are cut therefrom as desired, and the result is a superior fitting in the respects pointed out at the beginning of this specification.

I claim: a

A mandrel for making pipe bends, comprising a body having a straight cylindrical portion of less diameter than the interior diameter of the desired bend, a curved portion of uniform diam eter the same as theinterior diameter of the desired bend, and an intermediate curved portionconnecting said first-named and second-named portions and increasing in diameter from said side of said intermediate portion being curved first-named portion to said second-named porand of such curvature that the cross sectional tion, the outer side of said intermediate and said areasof said intermediate portion in successive second-named portions being of regular curva-' transverse planes equally spaced angularly about 5 ture and curved on an arc struck from a distant said center vary in diameter by substantially 5 center and merging into the outer side of said equal increments. first-named portion tangent thereto, the inner JAMES HALL TAYLOR. 

